Nowadays, in the rapid development of semiconductor storage device, DRAM, EEPROM, FLASH and other advanced storage devices have been widely used in computers and mobile communication terminals, attributed to their advantages such as high density, low power consumption and low price.
Due to the requirements of low power consumption and low cost, a power supply of the storage device always has a low voltage, such as 2.5V, 1.8V, etc. However, in order to implement “write”, “erase” and other operations of information, a programming voltage and an erase voltage which are much higher than the power supply voltage are always required, such as 8V, 12V, etc. Therefore, a charge pump circuit is widely used in the storage device. The charge pump circuit is used to obtain higher operation voltages for the storage device from the lower power supply voltage, such as the programming voltage, the erase voltage, etc.
A voltage division circuit is always used in a charge pump circuit, and is adapted for dividing a signal to be divided. A voltage division coefficient of the voltage division circuit stands for a ratio between a voltage value of the signal to be divided and a voltage value of the divided signal. In the voltage division circuit, multiple voltage division coefficients may be obtained by disposing the output terminal at different positions.
A structure diagram of a conventional resistor-type voltage division circuit is illustrated in FIG. 1. The circuit includes t resistors: R1 . . . Rt, which are connected in series, where an output terminal of a former one of every two adjacent resistors is connected with an input terminal of a latter one, an output terminal of a first resistor R1 is connected with ground, and an input terminal of the tth resistor Rt is adapted for receiving a signal to be divided V0. The voltage division circuit includes t−1 output terminals, such that it has t−1 voltage division coefficients and can output t−1 divided voltages V1 . . . Vt−1, where the ith divided voltage is equal to (i/t)V0. Different divided voltages at different voltage division coefficients can be obtained by connecting different output terminals.
However, in order to achieve a low current consumption, the above resistor-type voltage division circuit needs high resistors. The large resistors cost a large chip area and are harmful to miniaturization of the circuit.
A structure diagram of a conventional transistor-type voltage division circuit is illustrated in FIG. 2. The circuit includes t PMOS transistors R1 . . . Rt, which are connected in series, where a drain and a gate of a former one of every two adjacent PMOS transistors is connected with a source of a latter one, a source of the tth PMOS transistor Pt is adapted for receiving a signal to be divided V0, and a drain and a gate of a first PMOS transistor P1 is connected with ground. The voltage division circuit includes t−1 output terminals, such that it has t−1 voltage division coefficients and can output t−1 divided voltages V1 . . . Vt−1, where the ith divided voltage is equal to (i/t)V0. Different divided voltages at different voltage division coefficients can be obtained by connecting different output terminals.
However, in the above transistor-type voltage division circuit, if the value of the signal to be divided V0 is smaller than a sum of threshold values of the t transistors (about 0.7tV), the voltage division circuit cannot be turned on. Thus, all the PMOS transistors are in an off state, and all voltage division points are in a floating state. That is, the voltage division circuit cannot work properly.